This invention relates to a improved method of patterning a resist layer mounted on a semiconductor substrate or mask substrate.
Photolithography has hitherto been adopted as a method of patterning a resist layer deposited on the above-mentioned type of substrate for use as an etching mask. Particularly in recent years, demand is made to develop a method of producing high resolution structures with high throughput due to the high integration of a semiconductor element. In this respect, attention is paid to radiation lithography utilizing electron beams or X-rays.
The method of patterning a resist layer by radiation lithography comprises the steps of depositing a radiation-sensitive resist layer on a substrate; and emitting radiation on the resist layer to provide a pattern thereon, followed by development. Thereafter, the substrate is provided with a desired pattern by carrying out wet or dry etching with the patterned resist layer used as a mask. Accordingly, a radiation-sensitive resist layer used in radiation lithography should be formed of a material having the following properties:
(1) high sensitivity to radiation PA1 (2) high resolution PA1 (3) high resistance to an etchant, particularly to dry etching PA1 (4) good adhesion to a substrate
Various types of radiation-sensitive resist have hitherto been developed to meet the above-mentioned requirements. For example, a resist of the poly(olefin-sulfon) base and a resist of high molecular weight poly(methyl methacrylate) have already been reported as highly sensitive electron positive resists. Though highly sensitive to radiation, the former resist has the drawbacks that it has poor resistance to dry etching due to readiness for decomposition and has poor adhesivity to a substrate, and yet it is difficult to control various conditions for effecting high resolution. Though highly sensitive to radiation and moderately resistant to dry etching. The latter resist has the drawbacks that it is extremely difficult to uniformly coat said resist on the surface of a substrate due to its large molecular weight; a resist layer of uniform thickness can not be easily formed; and said resist more noticeably swells upon contact with a developer than a low molecular weight resist, thereby giving rise to a considerable decline in the patterning precision.
Other types of resist materials proposed to date include a mixture of two or more types of, for example, copolymers of methyl methacrylate and methacryloyl chloride and a single type of such copolymers, all said proposed resist compounds being cross-linked before application.
However, these proposed resist compounds have the following drawbacks:
(1) Since the resist compound consists of a single type or mixed type of the above-mentioned copolymers, it is necessary to precisely control the proportions of monomers constituting said copolymer or the ratio in which two or more types of said copolymer are mixed, because the proportions of the monomers and the ratio of said mixture delicately affect the degree in which a resist layer is cross-linked and consequently the etch-resistance and radiation-sensitivity of the resist layer;
(2) Since the conditions of cross-linking are difficult to control, the proposed resist material-producing process fails to be applied under a stable condition with high reproducibility; and
(3) A resist material prepared by the proposed process still has an insufficient radiation sensitivity.